Polyisocyanate compounds, process for producing the same, and optical materials using the same

ABSTRACT

The invention provides a novel polyisocyanate compound which is useful as a starting material for an optical material having a high refractive index, a low dispersion and excellent optical characteristics, and a process for producing this compound at good efficiency. The invention also provides an optical material having a high refractive index, a low dispersion, an excellent transparency without optical distortion and having good solvent resistance and weatherability.

[0001] This application is based on Japanese patent application Nos.H10-213570 and H10-213571, both filed on Jul. 29, 1998, the entirecontents of which are incorporated herein by reference.

FIELD OF THE INVENTION

[0002] The invention relates to a polyisocyanate compound and a processfor producing the same. In particular, it relates to a novelpolyisocyanate compound useful as a starting material for an opticalmaterial, and a process for producing the same at good efficiency. Italso relates to an optical material and an optical product using thesame. Specifically, it relates to an optical material which hasexcellent optical characteristics such as a high refractive index, a lowdispersion, an excellent transparency, lack of optical distortion andthe like, and which is also good in solvent resistance andweatherability, and to an optical product formed of this opticalmaterial, such as a lens, a prism, optical fibers, a substrate for arecording medium, a filter, a glass, a vase and the like.

BACKGROUND OF THE INVENTION

[0003] Recently, plastic materials have been used for optical parts inplace of inorganic glass, especially for eyeglass lenses, because theyare lightweight and have good dyeability and good impact resistance. Inparticular, a polyethylene glycol bisallylcarbonate polymer (hereinafterreferred to as CR-39) and polymethyl methacrylate (PMMA) have been used,primarily for plastic lenses. However, it has a refractive index of1.50, which is lower than that of inorganic glass. Therefore, when theyare used as lens materials, for example, the thickness of the lenses hasto be increased with the increasing power. Consequently, not only is thesuperiority of plastics as lightweight material been impaired, but alsothey have not been preferred in view of the aesthetic property.Furthermore, the concave lens, in particular, has had problems when thethickness (edge thickness) of the surrounding portion of the lens isincreased causing a birefringence or a chromatic aberration to occur.

[0004] For these reasons, in order to be able to decrease the thicknessof the lens while applying most of the characteristics of plasticshaving a low specific gravity, a plastic material having a highrefractive index has been in demand. As a material having such aperformance, for example, (1) a polymer comprising a xylene diisocyanatecompound and a polythiol compound (official gazette of JP-A-63-46213),(2) a resin comprising an aliphatic linear sulfur-containingdiisocyanate and a polythiol compound (official gazette ofJP-A-2-153302), (3) a polymer comprising a dithian derivativesubstituted with two isocyanatoalkyl groups and a polythiol (officialgazette of JP-A-4-159275) are disclosed.

[0005] Although the polymer of item (1) has an increased refractiveindex by limiting a combination with the polythiol compound to bepolymerized, it gives rise to problems that an Abbe number is decreasedand a chromatic aberration is increased.

[0006] Meanwhile, the resin (2) and the polymer (3) have a highrefractive index and the improvement in the chromatic aberration isfound therein, but they have a defect that a solvent resistance is poor.

[0007] Furthermore, since these prior art polymers are uncrosslinkedpolymers obtained from bifunctional isocyanate compounds, a specialcrosslinking agent is needed separately to improve a solvent resistance.Thus, the types of the polythiol compounds that can be polymerized arelimited.

SUMMARY OF THE INVENTION

[0008] In order to overcome many of the problems in the prior art, theinvention provides an optical material having the above-mentioneddesirable properties. It is a feature of the invention to provide anovel polyisocyanate compound that can give an optical material having ahigh refractive index, a low dispersion and an excellent solventresistance and weatherability, and a process for producing this compoundat good efficiency. It is also a feature of the invention to provide anoptical material which has excellent optical characteristics such as ahigh refractive index, a low dispersion, an excellent transparency, lackof optical distortion and the like, and which has good solventresistance and weatherability, and an optical product formed of thisoptical material.

[0009] In particular, the invention provides a polyisocyanate compoundhaving sulfur atoms, contributing to a high refractive index and a lowdispersion, in a main skeleton and having three isocyanates aspolymerization functional groups. In addition, the invention providesmethods for producing the polyisocyanate compound by an efficientprocesses. It also provides an optical material formed of apoly(thio)urethane obtained by subjecting a component comprising apolyisocyanate compound and a component comprising a compound having twoor more of hydroxyl groups or mercapto or both groups to a polyadditionreaction.

[0010] In one aspect, the invention provides a polyisocyanate compoundhaving general formula (I)

[0011] wherein n represents an integer from 1 to 4 and each of theindices n is the same.

[0012] In another embodiment, the polyisocyanate compound can beproduced by one of the following processes: production process 1,production process 2 and production process 3.

[0013] Production process 1 of the invention is a process for producinga polyisocyanate compound represented by general formula (I).

[0014] Process 1 comprises:

[0015] (a) reacting 1,2,3-trimercaptopropane with a halogeno-aliphaticcarboxylic acid lower alkyl ester represented by general formula (II)

X—CH₂—(CH₂)_(m)—COOR¹  (II)

[0016] wherein X represents a halogen atom, R¹ represents a lower alkylgroup, and m represents an integer of from 0 to 3, to obtain atricarboxylic acid ester represented by general formula (III)

[0017] wherein n and R¹ are as defined above,

[0018] (b) converting the tricarboxylic acid ester to a tricarbonylhydrazide represented by general formula (IV)

[0019] wherein n is as defined above,

[0020] and

[0021] (c) converting the carbonyl hydrazide group into an isocyanategroup.

[0022] Production process 2 of the invention is a process for producinga polyisocyanate compound represented by general formula (I).

[0023] Process 2 comprises:

[0024] (a) reacting a 1,2,3-trihalogenopropane with a mercapto-aliphaticcarboxylic acid lower alkyl ester represented by general formula (V)

HS—CH₂—(CH₂)_(m)—COOR¹  (V)

[0025] wherein R¹ represents a lower alkyl group, and m represents aninteger of from 0 to 3, to obtain a tricarboxylic acid ester representedby general formula (III),

[0026] (b) converting the tricarboxylic acid ester to tricarbonylhydrazide represented by general formula (IV)

[0027] wherein n is as defined above, and

[0028] (c) converting the carbonyl hydrazide group into an isocyanategroup.

[0029] Production process 3 of the invention is a process for producinga polyisocyanate compound represented by general formula (I-a)

[0030] wherein k represents an integer of from 0 to 2 and each of theindices k is the same.

[0031] Process 3 comprises:

[0032] (a) reacting 1,2,3-trimercaptopropane with an aliphaticunsaturated carboxylic acid lower alkyl ester represented by generalformula (VI)

CH₂=CH—(CH₂)_(k)—COOR²  (VI)

[0033] wherein R² represents a lower alkyl group, and k is as definedabove, to obtain a tricarboxylic acid ester represented by generalformula (VII)

[0034] wherein R² and k are as defined above,

[0035] (b) converting the tricarboxylic acid ester to tricarbonylhydrazide represented by general formula (VIII)

[0036] wherein k is as defined above, and

[0037] (c) converting the carbonyl hydrazide group into an isocyanategroup.

[0038] In another embodiment, the optical material of the invention isformed of a poly(thio)urethane, which is obtained by subjecting amonomer mixture comprising component (A) comprising at least apolyisocyanate compound represented by general formula (I), wherein nrepresents an integer of from 1 to 4, and component (B) comprising atleast one type selected from (a) a compound having two or more mercaptogroups in a molecule, (b) a compound having two or more hydroxyl groupsin a molecule and (c) a compound having one or more hydroxyl groups andone or more mercapto groups in a molecule to a polyaddition reaction.

[0039] The invention is to provide an optical product formed of theabove-mentioned optical material.

BRIEF DESCRIPTION OF THE DRAWINGS

[0040] The invention will be better understood by reference to theDetailed Description of the Invention when taken together with thedrawings, wherein:

[0041]FIG. 1 shows an ¹H-NMR spectrum of1,2,3-tris(isocyanatoethylthio)propane obtained in Production Example 1.

[0042]FIG. 2 shows an IR spectrum of1,2,3-tris(isocyanatoethylthio)propane obtained in Production Example 1.

DETAILED DESCRIPTION OF THE INVENTION

[0043] The polyisocyanate of the invention is a novel compoundrepresented by general formula (I). As is apparent from general formula(I), this novel compound has a structure in which sulfur atoms are boundto the 1-, 2- and 3-positions of propane, respectively, and threeisocyanate groups are further provided. Since the sulfur atoms are thusprovided in the structure, i.e., the basic skeleton, the refractiveindex and the Abbe number of the polyisocyanate compound itself areincreased. Accordingly, when an optical material is produced using thepolyisocyanate compound, the refractive index and the Abbe number of theoptical material are also increased. Furthermore, since thepolyisocyanate compound has three isocyanate groups, it also works as acrosslinking agent. Accordingly, when the optical material is producedusing the polyisocyanate compound, not only a high solvent resistancebut also a high heat resistance and excellent mechanical properties canbe imparted to the optical material without adding another crosslinkingagent as a secondary component. In the polyisocyanate compound, acompound in which n in general formula (I) is 1 or 2 is especiallypreferable.

[0044] When the polyisocyanate compound represented by general formula(I) is used, there is no need to use a crosslinking agent, but acrosslinking agent can also be used conjointly if required.

[0045] Examples of the polyisocyanate compound represented by generalformula (I)

[0046] are the following:

[0047] The process for producing the polyisocyanate compound representedby general formula (I) may be any process by which a polyisocyanatecompound having a desired structure can be produced. However, it can beproduced at quite good efficiency according to the processes 1, 2 and 3of the invention as mentioned below.

[0048] Production process 1:

[0049] In this production process 1, first, 1,2,3-trimercaptopropane isreacted with a halogeno-aliphatic carboxylic acid lower alkyl esterrepresented by general formula (II)

X—CH₂—(CH₂)_(m)—COOR₁  (II)

[0050] wherein X represents a halogen atom, R¹ represents a lower alkylgroup, and m represents an integer of from 0 to 3, to form atricarboxylic acid ester represented by general formula (III)

[0051] wherein n is an integer of from 1 to 4, each of the indices n isthe same and R′ is as defined above.

[0052] In this reaction, it is preferable that 1 mol of1,2,3-trimercaptopropane is reacted with substantially 3 moles of thehalogeno-aliphatic carboxylic acid lower alkyl ester represented bygeneral formula (II) in the presence of a hydrogen halide trappingagent. In this case, an appropriate solvent can be used as required.

[0053] The tricarboxylic acid ester represented by general formula (III)is reacted with hydrazine monohydrate or the like to lead the same to atricarbonyl hydrazide represented by general formula (IV)

[0054] wherein n is as defined above. At this time, a solvent such as alower alcohol or the like can be used as required.

[0055] Finally, the tricarbonyl hydrazide represented by general formula(IV) is reacted with nitrous acid in, for example, a hydrochloric acidaqueous solution to form carbonyl azide, and the heat transfer isconducted to convert a carbonyl azide group into an isocyanate group,whereby a desired polyisocyanate compound represented by general formula(I)

[0056] wherein n is as defined above, is obtained.

[0057] Production Process 2:

[0058] In this production process 2, first, the 1,2,3-trihalogenopropaneis reacted with a mercapto-aliphatic carboxylic acid lower alkyl esterrepresented by general formula (V).

HS—CH₂—(CH₂)_(m)—COOR¹  (V)

[0059] wherein R¹ represents a lower alkyl group, and m represents aninteger of from 0 to 3, to obtain a tricarboxylic acid ester representedby general formula (III)

[0060] wherein n and R¹ are as defined above.

[0061] In this reaction, it is preferable that 1 mol of the1,2,3-trihalogenopropane is reacted with substantially 3 moles of themercapto-aliphatic carboxylic acid lower alkyl ester represented bygeneral formula (V) in the presence of a hydrogen halide trapping agent.In this case, an appropriate solvent can be used as required.

[0062] Subsequently, the tricarboxylic acid ester represented by generalformula (III) is, as in the above-mentioned production process 1, led toa carbonyl hydrazide, and a carbonyl hydrazide group is then convertedinto an isocyanate group to obtain a desired polyisocyanate compoundrepresented by general formula (I).

[0063] Production Process 3:

[0064] The production process 3 is a process for producing apolyisocyanate compound in which n in general formula (I) is between 2and 4.

[0065] In this production process 3, first, 1,2,3-trimercaptopropane isreacted with an aliphatic unsaturated carboxylic acid lower alkyl esterrepresented by general formula (VI)

CH₂═CH—(CH₂)_(k)—COOR²  (VI)

[0066] wherein R² represents a lower alkyl group, and k represents aninteger of from 0 to 2, to obtain a tricarboxylic acid ester representedby general formula (VII)

[0067] wherein R² and k are as defined above.

[0068] In this reaction, it is preferable that 1 mol of1,2,3-trimercaptopropane is reacted with substantially 3 moles of thealiphatic unsaturated carboxylic acid lower alkyl ester represented bygeneral formula (VI) in the presence of a radical or anionic catalyst.In this case, an appropriate solvent can be used as required.

[0069] Subsequently, the tricarboxylic acid ester represented by generalformula (VII) is reacted with hydrazine monohydrate or the like to leadthe sane to a tricarbonyl hydrazide represented by general formula(VIII)

[0070] wherein k is as defined above. In this case, a solvent such as alower alcohol can be used as required.

[0071] Finally, the tricarbonyl hydrazide represented by general formula(VIII) is reacted with nitrous acid in, for example, a hydrochloric acidaqueous solution to form carbonyl azide, and the heat transfer isconducted to convert a carbonyl azide group into an isocyanate group,whereby a desired polyisocyanate compound represented by general formula(I-a)

[0072] wherein k is as defined above, is obtained.

[0073] Incidentally, the lower alkyl group indicated at R¹ and R² is amethyl group, an ethyl group, an n-propyl group, an isopropyl group orthe like.

[0074] The polyisocyanate compound represented by general formula (I)can also be produced by a phosgene method other than the above-mentionedprocesses of the invention.

[0075] The phosgene method is described by taking an example. First, 1mol of the 1,2,3-trimercaptopropane is reacted with substantially 3moles of a halogenoacetonitrile in the presence of a hydrogen halidetrapping agent to obtain 1,2,3-tris(cyanomethylthio)propane representedby formula (IX)

[0076] Then, the compound represented by general formula (IX) issubjected to hydrogenation to lead it to1,2,3-tris(aminoethylthio)propane represented by general formula (X)

[0077] Then, the compound represented by general formula (X) is reactedwith phosgene to obtain desired 1,2,3-tris(isocyanatoethylthio)propanerepresented by formula (I-b)

[0078] Component (A) may contain, to appropriately improve propertiesand the like of the optical material, one or two or more types of acompound having two or more isocyanate groups in a molecule other thanthe polyisocyanate compound represented by the above-mentioned generalformula (I). Specific examples of these compounds include o-xylenediisocyanate, m-xylene diisocyanate, p-xylene diisocyanate,α,α,α′,α′-tetramethyl-p-xylene diisocyanate,α,α,α′,α′-tetramethyl-m-xylene diisocyanate,1,3,5-tris(isocyanatomethyl)benzene, hexamethylene diisocyanate,1,4-diisocyanatobutane, isophorone diisocyanate, norbomene diisocyanate,bis(4,4′-isocyanatocyclohexyl)methane,1,3-bis(isocyanatomethyl)cyclohexane,1,3,5-tris(isocyanatomethyl)cyclohexane, 1,4-diisocyanatocyclohexane,1,3,5-triisocyanatocyclohexane, lysine triisocyanate,2,5-bis(isocyanatomethyl)-1,4-dithian, 1,3-dithiolan-4,5-diisocyanate,4,5-bis(isocyanatomethyl)-1,3-dithiolan, isocyanatomethyl sulfide,2-isocyanatoethyl sulfide, bis(isocyanatomethylthio)methane,1,2-bis(isocyanatomethylthio)ethane, bis(2-isocyanatoethylthio)methane,1,2-bis(2-isocyanatoethylthio)ethane,1,7-diisocyanato-2,4,6-trithiaheptane,1,5-diisocyanato-2-isocyanatomethyl-3-thiapentane,1,4-diisocyanato-2-isocyanatomethyl-3-thiabutane and the like.

[0079] The content of the polyisocyanate compound represented by generalformula (I) in the component (A) is preferably 0.1 mol % or more,especially preferably 5 mol % or more.

[0080] Component (B), another starting material of thepoly(thio)urethane, a component comprising at least one type selectedfrom (a) a compound having two or more mercapto groups in a molecule,(b) a compound having two or more hydroxyl groups in a molecule and (c)a compound having one or more hydroxyl groups and one or more mercaptogroups in a molecule is used.

[0081] Examples of the compound having two or more mercapto groups in amolecule as the component (a) here include2,5-bis(mercaptomethyl)-1,4-dithian, 2,5-bis(mercaptomethyl)-1,4-dithiandimer and polymer (trimer or higher polymer), 1,2,3-trimercaptopropane,tetrakis(7-mercapto-2,5-dithiaheptyl)methane, 1,2-ethanedithiol,1,3-propanedithiol, tetrakismercaptomethylmethane, 2-mercaptoethylsulfide, pentaerythritol tetrakismercaptopropionate, pentaerythritoltetrakismercaptoacetate, 1,2-benzenedithiol, 1,3-benzenedithiol,1,4-benzenedithiol, 1,3,5-benzenetrithiol, 1,2-dimercaptomethylbenzene,1,3-dimercaptomethylbenzene, 1,4dimercaptomethylbenzene,1,3,5-trimercaptomethylbenzene, toluene-3,4-dithiol,tris(3-mercaptopropyl) isocyanurate, 1,3-bis(mercaptomethyl)cyclohexane,1,4-bis(mercaptomethyl)cyclohexane, 2,2-bis(mercaptomethyl)-1,3-propanedithiol, 1,2-bis(2-mercaptoethylthio)-3-mercaptopropane,4,8-bis(mercaptomethyl)-3,6,9-trithia-1,11-undecanedithiol and the like.

[0082] Examples of the compound having two or more hydroxyl groups in amolecule as the component (b) include ethylene glycol,trimethylolpropane, glycerin, dihydroxybenzene, catechol,4,4′-dihydroxyphenyl sulfide, 2-hydroxyethyl sulfide, bisphenolA·propylene oxide 5-mol adduct, glycerin-propylene oxide 3-mol adductand the like.

[0083] Examples of the compound having one or more hydroxyl groups andone or more mercapto groups in a molecule as the component (c) include2-mercaptoethanol, 2,3-dimercaptopropanol,1,2-dihydroxy-3-mercaptopropane, 4-mercaptophenol and the like.

[0084] As component (B), a mercapto group-containing compound ispreferable. Especially, 2,5-bis(mercaptomethyl)-1,4-dithian and itsoligomer represented by general formula (I-a)

[0085] wherein p is an integer of from 1 to 20, and oligomers thereofare preferable.

[0086] With respect to the ratio of the component (A) to the component(B) in the invention, it is preferable that the molar ratio of theisocyanate group in the component (A) to the total amount of themercapto group and the hydroxyl group in the component (B), NCOgroup/(SH group+OH group), is in the range of from 0.95 to 1.05.

[0087] The monomer mixture comprising the component (A) and thecomponent (B) may contain one or two or more types of the compoundhaving two or more vinyl groups in the molecule to appropriately improvethe properties and the like of the optical material in addition to thecomponents (A) and (B). With respect to the ratio of these compoundsused at this time, it is preferable that the (isocyanate group +vinylgroup)/(mercapto group +hydroxyl group) molar ratio is in the range offrom 0.95 to 1.5 and the (vinyl group)/(isocyanate group) molar ratio is0.7 or less, and that polymerizable functional groups contained in thecomponent (B) are all mercapto groups. Specific examples of thesecompounds include 2,5-bis(2-thia-3-butenyl)-1,4-dithian, divinylbenzene,ethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate,a urethane-modified (meth)acrylate comprising at least two(meth)acryloxy groups in a molecule and the like. By the way, theabove-mentioned (meth)acrylate means both of an acrylate and amethacrylate, and the (meth)acryloxy group means both of an acryloxygroup and a methacryloxy group.

[0088] To the optical material of the invention can be added anultraviolet absorber, a coloring matter, a pigment and the like forimproving light absorption characteristics, an antioxidant, a colorationinhibitor and the like for improving a weatherability, and a releaseagent and the like for improving a moldability, as required.

[0089] Examples of the ultraviolet absorber include a benzotriazoletype, a benzophenone type, a salicylic acid type and the like. Examplesof the coloring matter and the pigment include an anthraquinone type, anazo type and the like.

[0090] Examples of the antioxidant and the coloration inhibitor includea monophenol type, a bisphenol type, a high-molecular phenol type, asulfur type, a phosphorus type and the like. Examples of the releaseagent include a fluorine-type surfactant, a silicone-type surfactant, anacidic phosphate, a higher fatty acid and the like.

[0091] A catalyst may be used, as required, to improve polymerization.For example, an amine compound, an organic metal compound and the likeare effective. Specific examples thereof include triethylenediamine,hexamethylenetetramine, N,N-dimethyloctylamine,N,N,N′,N′-tetramethyl-1,6-diaminohexane,4,4′-trimethylenebis(1-methylpiperidine),1,8-diazabicyclo-(5,4,0)-7-undecene, dimethyltin dichloride, dimethyltinbis(isooctylthioglycolate), dibutyltin dichloride, dibutyltin dilaurate,dibutyltin maleate, dibutyltin maleate polymer, dibutyltindiricinoleate, dibutyltin bis(dodecylmercaptide), dibutyltinbis(isooctylthioglycolate), dioctyltin dichloride, dioctyltin maleate,dioctyltin maleate polymer, dioctyltin bis(butylmaleate), dioctyltindilaurate, dioctyltin diricinoleate, dioctyltin dioleate, dioctyltindi(6-hydroxy)caproate, dioctyltin bis(isooctylthioglycokate),didodecyltin diricinoleate, copper oleate, copper acetylacetonate, ironacetylacetonate, iron naphthenate, iron lactate, iron citrate, irongluconate, potassium octanate, 2-ethylhexyl titanate and the like. Theabove-mentioned catalysts are effectively used either singly or incombination of two or more types.

[0092] When a vinyl compound is contained in the monomer mixture, theuse of an organic peroxide, an azo compound or the like other than theabove-mentioned catalyst is also effective.

[0093] An optical material using the polyisocyanate compound of theinvention can be produced. The following is but one example.

[0094] A uniform mixture of the component (A), the component (B), theadditives and the catalyst is subjected to a known cast polymerizationmethod. That is, it is cast into a die which is a combination of a glassor metal mold and a gasket made of a resin, and cured by heating. Inorder to expedite withdrawal of the resin after molding, the mold maypreviously be subjected to release agent treatment, or a release agentmay be added to the mixture of the component (A), the component (B) andthe like. The polymerization temperature varies depending on thecompound used. It is usually between −20 and +150° C. The polymerizationtime is between 0.5 and 72 hours. The optical material of the inventioncan easily be dyed in water or an organic solvent using an ordinarydisperse dye. At this time, for further expediting the dyeing, a carriermay be added or heating may be conducted. The optical material is usedas a plastic lens especially preferably, but is not limited thereto.

EXAMPLES

[0095] The invention is illustrated more specifically by referring tothe following Examples. However, the invention is not intended to belimited to these Examples.

[0096] The properties of the polyisocyanate compounds and opticalmaterials (polymers) were evaluated according to the following methods:

[0097] (1) ¹H-NMR spectrum (proton nuclear magnetic resonance spectrum):Measured using an FT-NMR Device EX 270 Model supplied by JEOL.

[0098] (2) IR spectrum (infrared absorption spectrum): Measured using aMAGNA-IR Spectrometer 560 Model supplied by Nicolet.

[0099] (3) Refractive index (n_(D)) and Abbe number (VD): Measured at20° C. using a precision refractometer KPR-200 Model supplied by Kalnew.

[0100] (4) Appearance: Visually observed.

[0101] (5) Weatherability: A lens (optical product using an opticalmaterial) was mounted on a weather meter fitted with a sunshine carbonarc lamp. When 200 hours passed, the lens was taken out, and the colorthereof was compared with that of the lens before the test. Theweatherability was evaluated according to the following standard.

[0102] ∘: unchanged

[0103] Δ: slightly yellowed

[0104] ×: yellowed

[0105] (6) Solvent resistance: A wiping test using acetone wasconducted, and the solvent resistance was evaluated according to thefollowing standard.

[0106] ∘: unchanged

[0107] ×: The surface is roughened or swollen.

[0108] (7) Optical distortion: Visually observed by the Schlierenmethod. The optical distortion was evaluated according to the followingstandard.

[0109] ∘: No distortion is observed.

[0110] ×: Distortion is observed.

Example 1 Production of 1,2,3-tris(isocyanatoethylthio)propane

[0111] 1,2,3-Trismercaptopropane (28.0 g, 0.20 moles) and 51.7 g (0.6moles) of methyl acrylate were dissolved in 300 ml of chloroform. TritonB (40% by weight methanol solution, 0.6 g) was added as a catalyst in anice bath, and the solution was stirred under reflux for 3 hours. Thereaction solution was allowed to cool, then washed with a dilute sodiumhydroxide aqueous solution and with water in this order, and dried overmagnesium sulfate. Thereafter, chloroform was fully removed to obtain71.5 g (0.18 moles) of colorless transparent1,2,3-tris(methyloxycarbonylethylthio)propane.

[0112] The ester compound was dissolved in 50 ml of methanol, and addeddropwise to a mixed solution of 81.0 g (1.62 moles) of hydrazinemonohydrate and 90 ml of methanol at room temperature. After thecompletion of the dropwise addition, the mixture was stirred at 70° C.for 4 hours. After the mixture was allowed to cool, white crystalsprecipitated were collected through filtration, and recrystallized frommethanol-water to obtain 69.4 g (0.17 moles) of1,2,3-tris(hydrazinocarbonylethylthio)propane.

[0113] The hydrazide compound was dissolved in 280 g of a 7.2% by weighthydrochloric acid aqueous solution, and 36.1 g (0.52 moles) of sodiumnitrite were added to a suspension with 160 ml of toluene. After thecompletion of the addition, the stirring was continued for 1 hour. Theorganic phase was extracted from the suspension, washed with water,dried (magnesium sulfate), and then heated to complete the transitionreaction. Toluene as a solvent was fully removed from the reactionsolution to obtain 46.0 g (0.13 moles) of a colorless transparentreaction product. This reaction product was identified to be a desiredpolyisocyanate compound from the ¹H-NMR spectrum and the IR spectrum.The ¹H-NMR spectrum of this novel polyisocyanate compound is shown inFIG. 1, and the IR spectrum thereof in FIG. 2.

Application Example 1

[0114] A mixture of 0.08 moles of 1,2,3-tris(isocyanatoethylthio)propane(designated SP-1 in Table 1) obtained in Example 1, 0.12 moles of2,5-bis(mercaptomethyl)-1,4-dithian dimer (designated DBMD in Table 1)and 1.2×10⁻⁴ moles of dibutyltin dilaurate (designated DBTDL in Table 1)was uniformly stirred, and cast into glass molds for forming a lens. Themixture was polymerized at 50° C. for 10 hours, then at 60° C. for 5hours and further at 120° C. for 3 hours to obtain a plastic lens. Theproperties of the resulting plastic lens are shown in Table 1. FromTable 1, it was found that the polymer obtained by using thepolyisocyanate compound of Example 1 was colorless and transparent, therefractive index (n_(D)) was as high as 1.69, the Abbe number (v_(D))was also as high as 36 (low dispersion), the weatherability and thesolvent resistance were excellent, and no optical distortion wasobserved.

Application Examples 2 to 6

[0115] The same procedure as in Application Example 1 was conductedexcept using a monomer composition comprising the polyisocyanatecompound SP-1 [1,2,3-tris(isocyanatoethylthio)propane] obtained inExample 1 or 1,2,3-tris(isocyanatomethylthio)propane (designated SP-2 inTable 1) as shown in Table 1 to obtain a plastic lens. The properties ofthese plastic lenses were shown in Table 1. From Table 1, it was foundthat the resulting plastic lenses were colorless and transparent, therefractive index (n_(D)) was as high as between 1.65 and 1.70, the Abbenumber (ν_(D)) was also as high as between 34 and 39 (low dispersion),the weatherability and the solvent resistance were excellent, and nooptical distortion was observed.

Application Comparative Example 1

[0116] A mixture of 0.06 moles of pentaerythritoltetrakismercaptopropionate (designated PETMP in Table 1), 0.12 moles ofm-xylene diisocyanate (designated XDI in Table 1) and 1.2×10⁴ moles ofdibutyltin dilaurate (designated DBTDL in Table 1) was uniformlystirred, and cast into glass molds for forming a lens. The mixture waspolymerized at 50° C. for 10 hours, then at 60° C. for 5 hours andfurther at 120° C. for 3 hours to obtain a plastic lens. The propertiesof the resulting plastic lens are shown in Table 1. From Table 1, it wasfound that the plastic lens in Application Comparative Example 1 wascolorless and transparent, no optical distortion was observed, and thesolvent resistance was excellent, but the refractive index was as low as1.59.

[0117] Application Comparative Examples 2 and 3

[0118] The same procedure as in Application Comparative Example 1 wasconducted except using monomer compositions shown in Table 1 to obtainplastic lenses. The properties of these plastic lenses were shown inTable 1. From Table 1, it was found that the plastic lens in ApplicationComparative Example 2 had a high refractive index of 1.68 and wasexcellent in the solvent resistance. However, it was colored yellow, theAbbe number was as low as 25, the weatherability was poor, and theoptical distortion was observed. Further, the plastic lens inApplication Comparative Example 3 was colorless and transparent, therefractive index was as high as 1.68, and no optical distortion wasobserved. However, the Abbe number was as low as 29, and the solventresistance was also poor. TABLE 1 Component (A) Component (B) CatalystSolvent Optical (mol) (mol) (mol) n_(D)/v_(D) Appearance Weatherabilityresistance distortion Application Example 1 SP-1 (0.08) DBMD (0.12)DBTDL 1.69/36 colorless, ◯ ◯ ◯ (1.2 × 10⁻⁴) transparent 2 SP-1 (0.04)BMMD (0.12) DBTDC 1.65/39 colorless, ◯ ◯ ◯ IPDI (0.06) (1.2 × 10⁻⁴)transparent 3 SP-1 (0.10) TMP (0.10) DBTDL 1.66/37 colorless, ◯ ◯ ◯ (1.5× 10⁻⁴) transparent 4 SP-2 (0.08) BMMD (0.12) DMTDC 1.67/36 colorless, ◯◯ ◯ (1.2 × 10⁻⁴) transparent ◯ ◯ ◯ 5 SP-2 (0.10) BMMC (0.06) DBTDL1.66/39 colorless, ◯ ◯ ◯ TMP (0.06) (1.5 × 10⁻⁴) transparent 6 SP-2(0.04) DBMD (0.12) DMTDC 1.70/34 colorless, ◯ ◯ ◯ IMTM (0.06) (1.2 ×10⁻⁴) transparent Application Comparative Example 1 XDI (0.12) PETMP(0.06) DBTDL 1.59/35 colorless Δ ◯ ◯ (1.2 × 10⁻⁴) transparent 2 TDI(0.12) XDT (0.07) DBTDL 1.68/25 yellow X ◯ X PETMA (0.025) (1.2 × 10⁻⁴)3 TPDI (0.10) XDT (0.10) DBTDL 1.68/29 colorless Δ X ◯ (1.0 × 10⁻⁴)transparent

[0119] The invention provides a polyisocyanate compound having aaliphatic chain comprising sulfur atoms as a basic skeleton, in whichthe refractive index and the Abbe number are high. It has threeisocyanate groups, and is easily polymerized with at least one type of acompound having two or more hydroxyl groups in a molecule, a compoundhaving two or more mercapto groups in a molecule and a compound havingone or more hydroxyl groups and one or more mercapto groups in amolecule to provide a three-dimensionally crosslinked optical material.Since the optical material obtained by using this polyisocyanatecompound contains the sulfur atoms in the main chain and is furthercrosslinked, the refractive index and the Abbe number are high, theweatherability, the solvent resistance and the transparency areexcellent, and no optical distortion is observed. The optical materialis preferably used in optical products, for example, lenses such as aspectacle lens, a camera lens and the like, a prism, optical fibers,substrates for recording medium used in an optical disk, a magnetic diskand the like, a filter and the like. It can also be used in ornamentalproducts such as a glass, a vase and the like which are obtained bymaking the most of the property of the high refractive index.

[0120] The descriptions presented herein enable a person of ordinaryskill in the art to make and use the invention. Although the inventionhas been fully described by way of examples with reference to theaccompanying drawings, it is to be noted that various modifications willbe readily apparent to those skilled in the art, and the genericprinciples defined herein may be applied to other embodiments andapplications without departing from the spirit and scope of theinvention. Thus, the invention is not intended to be limited to theembodiments shown, but is to be accorded the widest scope consistentwith the principles and features disclosed herein.

What is claimed is:
 1. A polyisocyanate compound of general formula (I)

wherein n represents an integer of from 1 to 4 and each of the indices nis the same.
 2. The polyisocyanate compound of claim 1, wherein said nis 1 or
 2. 3. A process for producing a polyisocyanate compoundrepresented by general formula (I)

wherein n represents an integer of from 1 to 4 and each of the indices nis the same, comprising: (a) reacting 1,2,3-trimercaptopropane with ahalogeno-aliphatic carboxylic acid lower alkyl ester represented bygeneral formula (II) X—CH₂—(CH₂)_(m)—COOR¹  (II) wherein X represents ahalogen atom, R₁ represents a lower alkyl group, and m represents aninteger of from 0 to 3, to obtain a tricarboxylic acid ester representedby general formula (III)

(b) converting the tricarboxylic acid ester to a tricarbonyl hydraziderepresented by general formula (IV)

and (c) converting the tricarbonyl hydrazide group into an isocyanategroup.
 4. A process for producing a polyisocyanate compound representedby general formula (I)

wherein n represents an integer of from 1 to 4 and each of the indices nis the same, comprising: (a) reacting a 1,2,3-trihalogenopropane with amercapto-aliphatic carboxylic acid lower alkyl ester represented bygeneral formula (V) HS—CH₂—(CH₂)_(m)—COOR¹  (V) wherein R¹ represents alower alkyl group, and m represents an integer of from 0 to 3, to obtaina tricarboxylic acid ester represented by general formula (III)

(b) converting the tricarboxylic acid ester to a tricarbonyl hydraziderepresented by general formula (IV)

and (c) converting the tricarbonyl hydrazide group into an isocyanategroup.
 5. A process for producing a polyisocyanate compound representedby general formula (I-a)

wherein k represents an integer of from 0 to 2 and each of the indices kis the same, comprising: (a) reacting 1,2,3-trimercaptopropane with analiphatic unsaturated carboxylic acid lower alkyl ester represented bygeneral formula (VI) CH₂═CH—(CH₂)_(k)—COOR²  (VI) wherein R² representsa lower alkyl group, to obtain a tricarboxylic acid ester represented bygeneral formula (VII)

(b) converting the tricarboxylic acid ester to a tricarbonyl hydraziderepresented by general formula (VIII)

and (c) converting the tricarbonyl hydrazide group into an isocyanategroup.
 6. A monomer mixture, comprising: component (A) comprising atleast a polyisocyanate compound represented by general formula (I)

wherein n represents an integer of from 1 to 4 and each of the indices nis the same, and component (B) comprising at least one compound selectedfrom the group consisting of (a) a compound having two or more mercaptogroups in a molecule, (b) a compound having two or more hydroxyl groupsin a molecule and (c) a compound having one or more hydroxyl groups andone or more mercapto groups in a molecule.
 7. The optical material ofclaim 6, wherein said n is 1 or
 2. 8. The optical material of claim 6 or7, wherein the compound having two or more mercapto groups in a moleculeis a compound represented by general formula (II-a)

wherein p represents an integer of from 1 to
 20. 9. The optical materialof claim 6 or 7, said material being optically transparent.
 10. Anoptical product formed of the optical material of claim 6 or
 7. 11. Theoptical product of claim 10, said product being spectacle lenses.
 12. Anoptical material formed of a poly(thio)urethane which is obtained byreacting the monomer mixture of claim 6.